The present invention relates to an image display apparatus used in a tomographic apparatus such as an X-ray CT (computed tomographic) apparatus or a magnetic resonance imaging system (MRI system).
In an imaging system of, e.g., an X-ray CT apparatus or an MRI system, an image display apparatus is used for displaying an image. For example, in an imaging system used in medical diagnosis, in place of a single still image, a series of image information of an identical part of an identical patient formed at different timings may have to be simultaneously displayed, or a plurality of image information of different patients, parts or processing methods may have to be simultaneously displayed. However, the conventional image display apparatus has only one display system and cannot effectively satisfy the above requirement.
When image data to be displayed has a matrix size larger than that of a display system, in the conventional image display apparatus, original image information is reduced so as to correspond to the matrix size of the display system, or a portion of the original image information is displayed and a displayed area thereof is appropriately switched so as to sequentially display the overall original image information. However, in the former case, i.e., in the case of reduction display, the reduced image cannot be subjected to detailed diagnosis. In the latter case, i.e., in the case of switching display of partial images, total observation cannot be made.
In the image display apparatus of this type, cine display (motion display) for displaying motion of a stomach or a heart as motion pictures is performed. The cine display of an image in, for example, a 512.sup.2 (512.times.512) matrix corresponds to sequential display of 20 to 30 still images per second. For the cine display in a conventional image display system, if a series of images (still images sequentially displayed to display each image for a predetermined period of time) to be recognized as substantially a one-frame still image is given to an image unit, image information corresponding to 20 to 30 still images of the 512.sup.2 matrix per image is stored in a memory, and the 20 to 30 still images stored in the memory are switched at high speed and displayed. Therefore, in order to perform cine display, a very large capacity memory must be used, and images stored in the memory must be switched at high speed and displayed. For this reason, it is very difficult to realize an image display apparatus.
Furthermore, when window processing is performed for the image information (gradation is provided in a specific gray level range of the original image data), a still larger capacity memory is required, and memory access becomes more complicated. Image write/read access with respect to the memory and window processing are performed by a common central processing unit (CPU). Therefore, an image display switching speed is considerably decreased. For this reason, it is additionally difficult to realize the image display apparatus.